Piston



W. C. M COY June 3, 1930.

PIST ON Filed Oct. 25, 1926 Timl.

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JS'VMsYM Q L L Patented June 3, 1930 .UNI-TED; sT -rEs PATENT OFFICE 'WILLIAM c.

MCCOY, OI SHAKER HEIGHTS, OHIO, ASSIGNOR TO THE CLEVELAND TRUST COMPANY, OF CLEVELAND, OHIO, A CORPORATION OF OHIO- Application filed mm as, 1926. Serial No. 14am.

This invention relates to pistons for internal combustion engines and particularly to composite pistons embodying. separately formed head and skirt elements.

One of the objects of this invention is to provide a iston structure of inexpensive design in w ich the head is formed of an aluminum alloy casting, or other light weight metal that is a relatively good conductor of heat, and the skirt separately formed of pressed steel or other suitable material.

Another object of the invention is to provide a piston structure having the advantages of the heat conductivity of aluminum and 15 the operational advantages of a skirt of relatively thin material of great strength, minimum weight, and of approximately the same coefiicient of thermal expansion as the cylinder in which the piston is to be used.

An additional object of the invention is to provide a head and skirt structure in which the skirt is pivotally related to the head in order that each element of thepiston may take separate adjustment relative to the cylinder'sleeve, to thereby minimize wear in .the ring grooves incident to tilting of the iston in the cylinder and to obtain uniform lsleiiring over the working'faces of the piston rt. 3 An additional object of the invention is to provide a skirt structure that may be formed of thin walled seamless steel tubing.

A further object of the invention is to provide a piston structure in which the temperature of the working faces of the skirt and the thermal enlargement of the skirt are primarily controlled by the temperature of the cylinder walls ofthe piston. Another object of the invention is to so con- 40 nect the piston skirt to the piston head as to substantially revent distortionsof the skirt through the t ermal expansion of the head. In the piston herein proposed, the head,

- with boss supporting portions inte ral therewith constitutes an independent y formed portion ofthe piston. This portion ofthe piston is herein referred to as the head element. It is preferably formed of an aluminum' alloy or of other material having physical characteristics that are particularly desirable for the head element. The piston skirt is preferably formed from thin walledseamless steel tubing or other desirable material that can be conveniently so cut and formed as to act as a cross head or guide for the side thrust imposed on the connecting rod. The'skirt element is formed of thin walled material that will more closely fol: low the temperature of the side wall of the cylinder and maintain a substantially uniform clearance at all operating temperatures. i

The various objects and advantages of.constructing pistons in accordance with this invention will be apparent from a consideraaccompanying drawings,

tion of the wherein Figure 1 is a side elevational view, looking in the direction of the boss, of the separately formed piston head and wrist pin connections therefor.

Fig. 2 is a side elevational view, taken transversely of the boss with parts broken away and shown in section through the wrist pin axis, of a piston structure constructed in accordance with this invention and embodying the formof piston head shown in Fig. 1.

Fig. 3 is an end plan view, with parts broken away and shown in section through one of the wrist pin bosses, of the skirt element of piston shown assembled with the piston head in Fig. 2.

Fig. 4 is a side elevational view of the piston skirt shown in Fig. 3 and taken in the direction of the wristpin boss.

Fig. 5 is a side elevational view, with parts broken away and shown in section through one of the boss elements, of a modified form of piston constructed in accordance with the invention.

Fig. 6 is a side elevational view, with parts broken away and shown in section through one of the boss elements, of a modified form of skirt structure that is adapted to be used in a piston of the character herein proposed.

Fig. 7 is a transverse sectional view of the piston skirt shown in Fig. 6 taken substan- Fig. 8 is a fragmentary top plan view of one of the skirt bosses. l

The piston head and skirt structure are independently formed of different materials.

The head structure, with boss supporting cylinder through the piston rings, and also in order that the head and boss supporting portions may be of very light weight although of great strength. The material should also be suitable for casting in permanent molds. Of the commercially known metals, aluminum and aluminum alloys are believed to mostadequately meet these requirements. The piston skirt, on the other hand,'is preferably formed of thin sheet steel that can be readily formed. The skirt could, however, be formed of other desirable wear resisting metals having thermal expansible charactertistics suitable for use in cylinders of different physical characteristics.

The head portion of the piston, which is particularly shown in Fig. 1, comprises a ring supporting portion with suitable ring grooves 1 that are formed therein, and .a wrist pm supporting boss portion 2 that is connected to the remainder of the structure hysuitable depending webs 3 that are respectively rein-.

forced by a strengthening rib 4.

The piston skirt, which -'s preferably formed of thin walled seamless steel tubing for use in cast iron or steel cylinder sleeves,

comprises a body portion preferably of cylindrical form that has inwardly bent portions 6 that constitute wrist pin supports for the skirt elements, The inwardly bent portions 6 are se arated from the cylindrical side wall of the tubing by transverse slots that ermit the ortions 6 to be pressed inwardl y to form t ereon a flanged boss carrying portion 7. The inwardly extending reinforcing flange 8 of the boss portion of the skirt is formed sufiiciently wide to properly support a wrist pin or a wrist pin hearing. The skirt structure is suflieiently rigid-to properly receive and transmit side thrust from the connecting rod to the cylinder wall without material distortion. The skirt portion is preferably pivotally related to the head in order that the only stresses that are imposed thereon are the side thrusts that are transmitted directly from the wrist pin to the skirt portion of the piston in the manner of operation of the cross head of the conventional form of reciprocating steam engine.

In the piston structure shown in Fig. 2 which embodies a head structure of the form shown in Fig. 1' and skirt structure of the form shown in Figs. 3 and 4 in assembled relation, a bushing 9 is mounted solely in the boss supporting portion 7 of the skirt to provide a suitable bearing for the wrist pin of the skirt that is entirely independent of the operation of the head. The maximum diameter of the boss carrying portions 2 of the head is sufliciently small to permit the piston head structure to be inserted through the open upper end of the skirt in order that the supporting boss element 7 of the skirt will lie within the boss portions 2 of the head. This is desirable in order that the thermal expansion of the head will not carry the boss su" porting. portions 2 of the skirt outwardly therewith. In this form of piston, the use of a floating wrist pin, that is locked in place by some form of'conventional spring rin adapted to be received in the grooves 10 oY the boss portions 2 of the piston head, is preferred.

In the piston shown in Fig. 2 the skirt is independently supported from the wrist pin, and the piston head is pivotally related to the skirt in order that the only forces that are imposed upon the piston head will be longitudinally of the cylinder and also in order that there will be substantially no movement of the ring supporting portion of the piston headincident to the lateral tilting of the piston in the cylinder.. In the piston proposed, lateral shifting of the wrist pin incident to skirt clearances causes the head to pivot about the ring supporting portion thereof without substantial lateral shifting of the head.

In the conventional form of piston, the lateral side thrust that is taken by the 0pposed working faces of the'skirt causes .lat-

eral shifting of the piston body with the greatest range of movement in'the zone of the ring carrying portion of the head. The lateral shifting of the piston rings in the r ng grooves during operation necessarily accentuates the wear between the rings and the ring grooves.

' In the piston structure herein proposed, there is substantially no lateral shifting of the ring carrying portion of the iston head, and therefore there is substantia 1y no movement of the piston rings in the ring grooves of the head except the movement incident to adjustment of-the rings to differences in the cylinder bore. Such movement of the rings in the ring grooves is relatively small as compared with the movement incidental to lateral shifting of the piston head in the cylinder in response to side thrust against the skirt of the piston when the head and skirt are rigidly connected together. This'is particularly important in pistons formed of aluminum and other light weight metal in which wear results from the movement of the piston ring in the ring grooves.

The form of piston shown in Fig. 5 has the skirt and of the head. The bushing 11 is preferably a pressed fit in the skirt boss 7 and pivotally' mounted in the boss supporting portion 2-of thehead. This pivotal relation between the piston head and the skirt provides bearing parts, wherein the more expansible and hotter operating part l-ies out- 10 side of the bushing to thereb prevent bindin between the parts fromeat. 7

it may be preferred, however, to pivotally mount the skirt portion 12 on the bushing 11 and to press the bushing 11 tightly within the boss supporting portion of the head in order to obtain greater bearing area for the boss elements of the head. This form of pivotal connection is desirable if a split bronze skirt, such as that illustrated in Fig. 2 7, is used or if therpiston skirt is of bronze for use in a cylinder of alumin alloy or of other relatively high expansililgmaterial In the form of skirt shown in Fig. 5, a series of longitudinal slots 13 are provided in 5 each of the connecting members that join the working faces of the piston skirt. These longitudinal slots relieve the'tightening of the skirt in the cylinder sleeve through the flexibility of the boss supporting portions 6 so of the skirt to thereby prevent binding of the piston skirt within the cylinder sleeve.

' If desired, the piston skirt may also be formed with a longitudinalslot 15 extending the entire length of one working face of the piston skirt as shown in Fig. 6. A skirt of this character is adapted to be supported from a bushing of the character shown in Fig. ,5 that has a working fit within the skirt or the boss element of the head, or from a bushing 9 of the character shown in Fig. 2.

. An inwardly extending reinforcing flange 14 is preferably formed on the end portion of the skirt remote from the head, and a cor responding flange 14', with parts cut away to admit the boss portions of the head, is formed on the upper end of the skirt. These flanges serve to stiffen the skirt and also to maintain the skirt in cylindrical form at all times. Such flanges can readily be formed on the dpiston skirt by spinn'- ,g or other desire process prior to the ongitudinal sliti ting of the piston skirt.

It will be evident from a consideration of the piston structure herein described, that the skirt of the'piston may be fitted as closely to the cylinder wall as the metal from which the skirt is formedwarrants. This thin will of the skirt and the separable character of the element.

wardly. If desired, the piston sleeve shown in Fig. 6 could be formed without a'transverse slot underlying the boss by stretching the metal of the skirt to form the boss The method of manufacture of the skirt from short lengths of steel or other metal tubing, by the process of progressively pressing the side wall of the tubing inwardl as the transverse-cut is extended to form oss carryin elements of the skirt from the side walls 0 the tube, is import-ant. This is an inexpensive operation that provides a piston of accurate dimension, of great strength although sufiiciently flexible to follow irregularities inthe cylinder sleeve. Tubing suitable for such use can be had in relatively accurate sizes and, for engines of the less expensive design, the piston skirt could be formed as shown in Fig. 6 and the skirt used in the .engine substantially without prior. grinding. The piston skirt could be sprung into the cylinder and caused to free itself by working. in of the engine. As heretofore stated,"the material from which thesleeve is formed is primarily dependent upon the hysical character of the piston skirt se ected and the material'of the cylinder sleeve. In a piston sleeve of the form shown in Fig. 6, the yielding character of the piston skirt will accommodate mechanical tolerances in the manufacture of cylindrical sleeves.

Since the head of the piston is separately formed and since it does not-involve any intricate coring, the expense'of the casting of the head of the piston will be greatly reduced. The skirt of the'piston, on. the other hand,

being formed of any desired character of metal that is suitable for this use, may be made of thin walled material that is very light in weight and that will be of such expansible character as to properly fit the cylinder wall with the desired clearance.

It will also be apparent to those skilled in the art thatihe general form of the piston, independent of the pivotal' relation of the head and skirt, and the method of its manufacture, is of considerable importance. In

fact, if desired, the bushing element 11 could be used to rigidly unite the head and skirt elements. T is is particularly true of the plston shown'm Fig. 5 and-Fig. 6.

If the plston'head and skirt are rigidly secured together by the bushing 11, of Fig.

5, it is then preferable to form the skirt of a suitable wear resisting brofizealloy of higher temperature coeflicient of expansion than the cylinder in order that the separation of the ,boss elements of the skirt in response to thermal expansion of the head will not tendto draw the thrust faces of the skirt toward each other as is well known inthe art.

- Bushings 9 or 11, for use in the piston, could be of die cast material, the fit ofwhich is within allowed manufacturing tolerances.

Although I have described only a few preferred modifications of the invention, many other adaptations thereof can be produced without departing from thespirit orscope of the invention. I desire','"tlierefore, that only such limitations shall be imposed on the invention as are set forth in the accompanyingclaims.

What I claim is:

1. A composite piston structure having a separately formed head provided with depending wrist pin bosses, a sheet metal skirt, inwardly oifset portions formed in opposite Walls of said skirt, and wrist pin bosses formed in said ofiset portions and adapted to be disposed between said bosses in said head.

2. A composite piston structure having a separately formed head provided with depending wrist pin bosses, a sheet metal skirt, inwardly'oifset portions formed in opposite walls of said skirt and having coaxial openings therein, and circular wrist pin supporting flanges integral with said ofi'set portions and defining said coaxial openings, said wrist -pin supporting flanges being disposed between said bosses in said head.

3. A composite piston structure having a separately formed head provided with depending wrist pin bosses, a sheet metal skirt provided with spaced transverse slots at opposite sides thereof, the portions of said skirt etween said slots being inwardly bent and provided withcoaxial openings, circular flanges integral with said inwardly bent portions and defining said openings, said flanges being disposed between said bosses in said head, and a wrist pinbushing extending through said bosses in said head and said circular flanges for pivotally connecting said head and skirt.

4. A composite piston structure having a separately formed head provided with depending wrist pin bosses, and a tubular skirt of a different metal provided with apair of spaced transverse slots in opposite sides thereof, the portions of said skirt between said spaced slots being oflset inwardly with respect to said skirt and provided with 00- axial wrist pin receiving openings, said wrist pin bosses on said head being disposed between said ofiset portions and the circular portions of said skirt in axial alignment with said openings in said ofl'set portions for receiving a wrist pin.

5. A composite piston structure having a separately formed head provided with depending wrist pin bosses, a sheet metal skirt provided with a pair of spaced transverse slots in opposite sides thereof, the portion ofsaid skirt in each side between said spaced lots being inwardly offset with respectto the circular portion thereof and provided with an'opening, and circular wrist pin support ing flanges integral with said oflset portions and defining the said openings therein, said depending wrist pin bosses being positioned between the walls of said skirt and said ofiset portion in axial alignment with said openmgs.

6. A tubular sheet metal skirt for a piston having a separately formed head, said skirt having a pair of spaced transverse slots in diametrically opposite faces thereof, the metal in each of said faces between said spaced slots being ofiset inwardly with respect to the metal above and below said slots and provided with a wrist pin receiving opening, and the metal defining said opening bein bent perpendicular to said ofiset portion.

in testimony whereof I aflix my signature.

WILLIAM C. MoCOY. 

